1. Field
The present inventions relate generally to batteries and methods of making the same.
2. Description of the Related Art
Metal-air batteries (such as zinc-air batteries) are frequently used in hearing devices because of their volumetric energy efficiency. Such batteries can be a challenge to design and manufacture because the cathode must have access to oxygen (i.e., air) and the electrolyte solution, commonly a very slippery sodium hydroxide solution or potassium hydroxide solution, must be contained within the battery can without leaking. The conventional method of containing the electrolyte within the battery involves crimping cathode assembly into an anode can with a sealing grommet between the two. Due to the challenges associated with mass production, the most common crimped battery is the button battery, which includes short, cylindrical anode and cathode cans that can be stamped (or drawn) and crimped uniformly. Commonly assigned U.S. Pat. No. 6,567,527 (“the '527 patent”) discloses a zinc-air battery that has a bullet-shaped battery can with an aspect ratio, i.e., the ratio of the length to the maximum dimension of the cross-section, that is higher than that of a button battery. The higher aspect ratio of the battery can is especially useful in, for example, deep in the canal hearing aids. The battery can in the '527 patent has an internal retention ledge to support the air cathode. The air cathode is crimped into the battery can while the battery can is supported from below. The crimp force must not, however, exceed the buckling strength of the bullet-shaped can, which limits the aspect ratio and the ability to form a leak tight seal. More recently, batteries having cans with inwardly extending neck portions that define external retention ledges that facilitate the use of still higher aspect ratios and greater crimping force (for improved sealing at the grommet) have been introduced. Examples of such batteries, which are especially useful in extended wear hearing devices that are worn completely in the bony region of the ear canal, may be found in commonly assigned U.S. Pat. No. 8,761,423.